Deflection Circuit; Video Circuit; Power Supply - Tatung VM9G5DA S995T Service Manual

Colour monitor flat screen

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5-2 DEFLECTION CIRCUIT

Hor. Sync. And Ver. Sync come from PC, then go into the CPU (IC101). The output Sync Flows into Auto sync Deflection

Controller IC401 (TDA4856). The IC401 processes Sync Signal and output drive signal to horizontal, vertical and B+ driver

circuit. IC401 also generates some certain waveforms for usage of geometry correction, such as H-size, V-center etc. by DC

current or voltage control. Thus the geometry can be controlled automatically or manually.

IC601 (TDA4866) is a full bridge current driven Vertical deflection booster. R626 connected in series with the deflection

coil provides internal feedback information. The differential input circuit is voltage driven, R629 connected between the

differential input, determines the output current through the deflection coil.

Q424, Q425,Q409,Q411,Q402, T401 are Horizontal drive circuit, Q403 is an H-output transistor. Q404, Q405, Q406, Q407

are Horizontal size control circuit. Q427, RY401 to change retrace time of horizontal, the switch frequency is 66KHz.

IC403, IC404, Q412,Q417,Q420,Q419,Q418 to switch the Cs capacitor. L401 is a linearity correction coil. Q708, T701 are

Hor. And Ver. Dynamic focus circuit.

Q705, Q706 generate the vertical blanking signal output to G1 of CRT, Q703, Q707 are brightness control transistor, Q416

is also for MUTE control.

IC801 is a three channel video preamplifier with OSD Mixing, PIN 5, 8, 11 are video input, the signal recommended is equal

to 0.7Vp-p, PIN 1, 2, 3, 4 are OSD signal input. The luminosity of OSD was determined by PIN 25, PIN 15 is clamping

signal input, that to restore the DC voltage of video signal. Video output from pin 18, 20, 23 and couple to the R.G, B,

Amplifier Q802, Q805, Q803, Q806, Q804,Q807, directly,Q817, Q818, Q818, are R.G.B bias control, which to set the black

level.

The design uses a discontinuous fly back topology operating in current-mode resulting in a multiple output switcher with

stack well. Faster diodes are used. The fast transient response of the control loop maintains picture integrity. Very fast

current limiting protects the switcher against short circuits.

UC3842AM is the current mode controller selected. It offers feed forward compensation, feedback error amplifier, and low

voltage lock out features, IC901, T901, Q901 are a main power supply circuit, that provide 80V, 54V, 30V, 20V to the

deflection and video circuit, and provide 5V through Q906 to MCU.

The FET starts a cycle by allowing current to flow into the primary of the power transformer. As current ramps up with time,

the voltage across the current sense resistor (R929) also ramps to a point where the UC3842 determine that enough power is

stored and turns off the FET. As the voltage on the transformer reverses, power is dumped from the main power transformer

through diodes into the different supplies. To keep RFI to a minimum and reduce transistor heating, a turn-off snuffer

network is placed across the FET. Current from the secondary windings are rectified and filtered to create the desired

voltages. Small high current capacitors quickly return charging current to the source. Filter inductors remove high frequency

noise.

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